Sensor array

ABSTRACT

A sensor is used to detect a substance component in an aqueous solution. This sensor has electrically conducting and mutually insulated electrodes (7) which can be connected to a data-recording device. A sensor membrane array responsive to substance components to be detected includes several individual membranes (2) in rows or row-column arrays mounted on a flat support (1).

This is a continuation of application Ser. No. 08/203,950 filed Mar. 1,1994 and now abandoned.

FIELD OF THE INVENTION

This invention relates to a sensor for selectively detecting ormeasuring at least one substance component in an aqueous solution.

BACKGROUND OF THE INVENTION

Sensors of the general type to which the invention relates have beenused in large numbers in chemical engineering, in analysis and morerecently also in medicine. In medicine in particular there is a greatdemand for such so-called bio-sensors. Biosensors are most widely usedin diabetes therapy. Examples are found in U.S. Pat. Nos. 4,545,382 and4,711,245, Higgins. Essentially, they consist of disposablegluco-sensors onto which a small quantity of blood to be analyzed isdeposited and which are plugged into a measuring device (glucometer).The user conventionally withdraws the required blood by piercing afinger tip. When the gluco-sensor is inserted into the measuring device,the bio-membrane of the sensor makes electrical contact with the deviceas a result of which voltage and/or current changes in the activebio-membrane caused by the different glucose contents are transmitted tothe measuring device. Further details of such known glucometers andgluco-sensors are discussed in Graetzel et al WO92/14,836.

All the known sensors of this kind incur the drawback of short life andcomparatively costly manufacture. In particular it was found that thegluco-sensor's membrane, of which the active ingredient is an unstableenzyme such as glucose oxidase, on one hand is difficult to reproduciblymanufacture and on the other hand its properties change with age so thatits usable life is much degraded. Examples of such enzymes andcombinations of them with a mediator are given in the Graetzel et aldocuments WO92/14,836 and WO92/14,741.

SUMMARY OF THE INVENTION

An object of the invention is to create a sensor for detecting anelectrical current produced by reaction with the sensor to evaluatechemical substances participating in the reaction which evinces extendedlife and at the same time is substantially more economical tomanufacture.

Instead of providing the patient with a pack of several hundreddisposable individual sensors, a single sensor may be used whichcomprises a plurality of individual sensor membranes mounted in rows ora matrix of row-column arrays on a flat substrate.

The advantages achieved by the invention essentially are that veryeconomical manufacture is made possible by the sensor of the inventionand in that its useful life is extended.

BRIEF DESCRIPTION OF THE DRAWIGNS

Preferred embodiments of the invention are described below withreference to the following drawings wherein:

FIG. 1 is a perspective view of a sensor in accordance with theinvention with sensor membranes along a linear measuring strip;

FIG. 2 is a transverse sectional view of the sensor of FIG. 1;

FIG. 3 is a schematic view of a typical measuring device with a sensorin accordance with FIG. 1 inserted therein;

FIG. 4 is a transverse sectional view of a further embodiment of asensor in accordance with the invention;

FIG. 5 is a transverse sectional view of another embodiment of a sensorin accordance with the invention;

FIG. 6 is a transverse sectional view of yet another embodiment of asensor in accordance with the invention; and

FIG. 7 is a perspective view of a sensor in accordance with theinvention in the form of a row-column matrix.

DESCRIPTION OF THE PREFFERED EMBODIMENTS

A sensor assembly in accordance with the invention is shown in FIG. 1and comprises an elongated and flat substrate 1 of plastic such aspolyvinyl chloride (PVC) on which several individual sensor membranes 2are mounted in a row and are covered by a removable aluminum foil 3protecting them against external influences. Each individual membrane 2essentially consists of an enzyme-mediator combination capable ofresponding to the substance component which must be detected and, bymeans of a set of electrodes 7 mounted laterally of each membrane on thelongitudinal substrate 1, the adjacent membrane can be connected to adata-recording or display device 4 as shown schematically in FIG. 3.Basically the set of electrodes 7 includes at least two, but preferablythree, mutually insulated electrodes, including an operating electrode,a monitoring electrode and a reference electrode, the latter preferablybeing made of silver. If only two sensors are provided, the referenceand monitoring electrodes are combined into one.

To activate an individual membrane 2, it suffices to manually remove thepart of the protective layer over it, for instance by tearing it off,piercing or punching it, and to deposit thereon the aqueous solution,for instance a blood drop, to be tested.

Thereupon the sensor assembly with the individual membranes 2 arrangedin a row can be inserted in a known manner into a data-recording anddisplay device 4 schematically shown in FIG. 3. The sensor activationcan be implemented in several ways. One way is to insert the sensorassembly into the data-recording and display device 4 until the selectedindividual sensor membrane 2 makes contact by its electrodes 7 withsensor electronics, not shown, of the data-recording and display device4. Another way, applicable especially to sensors implanted into thebodies of patients, is to control the next individual membrane 2 to beactivated by the sensor electronics of the data-recording and displaydevice 4 itself. More details on data-recording and display device 4 aswell as on the construction of individual membranes 2 will be found inthe Swiss Michel patent 677,149 which is hereby incorporated byreference.

As regards sensors outside the body, used individual membranes 2 may besimply broken off and discarded.

A somewhat more complex sensor assembly is shown in FIG. 4, where asubstrate 1 supports a plastic substrate layer 8 into which areintegrated a plurality of individual membranes 2, again mounted in arow, together with a superposed calibration liquid 5 and a removablealuminum foil layer 3 providing protection against external effects andcovering this assembly. Calibration liquid 5 includes a neutral saltsolution and performs several functions. In the first place, it allowsstoring the individual membranes 2 in a defined environment and in thesecond place it allows calibrating when starting the data-recording anddisplay device 4. The third function, which is particularly advantageousfor the invention, is that by heating the calibration liquid 5,similarly to an ink-jet printer, the protective layer 3 can be burstopen by internal energy provided by the vapor pressure of the liquid toremove the foil and activate the individual membranes 2 for measurement.

For design reasons, a further plastic substrate layer 8 is mounted onthe substrate I for the embodiment of the calibration solution 5 of FIG.4, and the protective layer 3 rests on substrate layer 8.

FIG. 5 shows another embodiment of the sensor of FIG. 4, wherein anabsorbent foil or cover 6 is between each individual membrane 2 and thecalibration liquid to optimize the distribution of the aqueous solutionto be measured. A nylon netting or porous foil may be used as absorbentcover 6, the purpose of which is to retain and spread a small amount ofliquid.

FIG. 6 shows a preferred embodiment of the sensor of the invention inwhich the individual membranes 2 together with a superposed suction duct6 covered by the protective foil 3 are mounted on the substrate 1. Thisis the least expensive and simplest of the embodiments.

FIG. 7 shows a sensor in the form of a multi-row array of individuallymounted individual membranes 2_(m),n (individual membrane of the mth rowand nth column). This array is especially suitable for implant sensorsin which individual membranes 2 to be activated are directly controlledby data-recording and display device 4 electronics also making thecalibration liquid 5 boil.

What is claimed is:
 1. An array of sensors for selectively detecting ormeasuring at least one substance component in an aqueous solution,comprisinga flat substrate (1); a plurality of sets of electricallyconductive and mutually insulated electrodes (7) on said substrateconnectable to a data-recording and display device (4); an array ofindividual sensor membranes each responsive to a component of asubstance to be detected or measured, said array of individual sensormembranes (2) being arranged on said flat substrate (1) with onemembrane adjacent each set of electrodes; a protective layer coveringand protecting said membranes against external influences; a calibrationsolution (5) between said individual membranes and said protectivelayer; and an absorbent cover mounted on each of said individualmembranes.
 2. A sensor according to claim 1 wherein said protectivelayer is removable and comprises a metal foil.
 3. A sensor according toclaim 1 wherein said calibration solution comprises a neutral saltsolution.
 4. A sensor according to claim 1 wherein each of saidindividual membranes (2) contains an enzyme responsive to the substancecomponent to be detected.
 5. A sensor according to claim 4 wherein, inaddition to said enzyme, each of said individual membranes (2) comprisesa mediator.
 6. A sensor according to claim 1 wherein each of saidindividual membranes (2) responds to physiological substances in thebody fluids.
 7. A sensor according to claim 6 wherein a fluid to whichsaid membrane responds is glucose.
 8. A sensor according to claim 1wherein said electrodes (7) include three mutually insulated electrodesincluding an operational electrode, a monitoring electrode, and areference electrode, said reference electrode being made of silver.